Approaching ultimate flexible organic light-emitting diodes using a graphene anode

Ultimate flexible organic light-emitting diodes (OLEDs) should have an ultra-high device efficiency, a low-efficiency roll-off at a high luminance and excellent flexibility. Here, we realized flexible tandem OLEDs using a graphene anode with a very high electroluminescent efficiency of ~205.9 cd A −1 , 45.2% (~396.4 cd A −1 , 87.3% with a hemispherical lens) and a very low efficiency roll-off at a high luminance of ~6.6% at 10 000 cd m −2 (~3.8% with a hemispherical lens) by stacking two organic electroluminescence (EL) units. For the first time, we used an easily controlled and low-temperature processable charge generation layer with lithium nitride (Li 3 N). This simultaneously provided efficient stacking of EL units and enhanced compatibility of the flexible device on a thin plastic substrate. The flexible tandem OLEDs with a graphene anode also showed great flexibility against bending up to a bending strain of 6.7%. These results represent a significant advancement towards the production of next-generation flexible displays and solid-state lighting that use a graphene anode. Organic light-emitting diodes: graphene flexes its capabilities Bendable displays with nearly unmatched strain resistance and device efficiency can be realized using graphene-based transparent electrodes. Organic light-emitting diodes (OLEDs) are integral to today's touch-screen technology, but future applications are limited by a reliance on brittle, indium tin oxide electrodes. Researchers led by Tae-Woo Lee from Pohang University of Science and Technology in South Korea have made an alternative OLED prototype that assembles multi-electroluminescent units of organic materials onto high-quality, graphene electrodes transferred to thin plastic substrates. The team improved on previous graphene OLED designs by inserting a charge-generation layer - an organic material mixed with lithium ions that can be evaporated at low temperatures - between separate electroluminescent stacks. This setup provides ample charge carriers and mechanical strength to keep the OLED efficiency high, even after 1,000 bending cycles. We realized highly flexible tandem OLEDs using a graphene anode with very high electroluminescent efficiency ~205.9 cd A −1 , 45.2% (~396.4 cd A −1 , 87.3% with a hemispherical lens) and very low efficiency roll-off at high luminance ~6.6% at 10 000 cd m −2 (~3.8% with a hemispherical lens) by stacking two organic electroluminescence units using a easily controllable and low-tem